The present invention relates, in general, to tremolo devices for pipe organs, and more particularly to a motor driven tremolo arm which is pivotally mounted at one end and interconnected with the wind supply for the organ so that a reciprocating motion of the free end of the tremolo device produces a periodic pressure variation in the wind supply to produce the desired tremolo effect in the sound produced by the organ pipes.
It has long been known in the pipe organ art that tremolo effects can be produced in the speech of organ pipes by varying the pressure of the air supplied to those pipes. Such variations in air pressure cause corresponding variations in the amplitude and frequency of the sound produced by the pipes, with the sound from all of the pipes varying at the same time to produce a pleasing effect in the overall sound of the organ.
One of the early techniques utilized in the production of tremolo, and a technique that is still commonly in use, is the provision of a dump valve which periodically vents pressurized air from the air supply of the organ. Although such a dump valve can be located elsewhere in the air supply system, it is usually found in the air pressure regulator, either mounted directly on the regulator box, or connected thereto by a short conduit. The pressure regulator is a variable reservoir which receives air from a suitable source of supply, such as a large blower fan, and directs the air to the wind chest which directly supplies air to the pipes. The regulator includes a bellows arrangement which is biased in accordance with the pressure to be maintained. The bellows collapses as pipe stops are opened to draw air out of the wind chest to thereby maintain the desired air pressure, and expands when the pipe stops are closed. Although the bellows is in substantially constant motion during the playing of the organ, the air pressure within the system remains essentially constant so that the pipes will remain in tune.
The dump valve tremolo devices operate periodically to release air from the pressure regulator reservoir, thereby to superimpose on the air flow variation in pressure which are too rapid for compensation by the bellows and which thereby produce tremulant variations in the sound produced by the organ pipes. The dump valve is essentially a resonant device which, when activated, alternately opens and closes at a periodic rate which depends upon the design of the valve. Such devices are well known in the prior art, and are illustrated in patents such as U.S. Pat. No. 478,552 to Basset, No. 797,719 to Challinor, No. 1,243,644 to VanValkenbeurg, No. 1,262,640 to Cloetens, and No. 2,633,047 to Glatter-Gotz.
Although tremolo devices of the dump valve type have been used in the art for many years, they have not been entirely satisfactory, since they reduce the amount of air available to operate the pipes, and thus require a larger air supply than would normally be necessary. This increases the cost of the organ, requires additional space for installation, and increases the amount of noise produced by the air supply fan. Further, such tremolo devices often produce effects which change with the amount of air being delivered to the organ. Thus, a chord with a large number of notes played at one time may have a different tremolo than is produced when only one or two notes are played, and this may produce undesirable results. Furthermore, these devices are complex, and can easily get out of adjustment, as for example, with changes in ambient temperature.
A solution to many of the difficulties encountered with the dump valve arrangement was provided a number of years ago with the introduction of a motor-driven counterweight device mounted directly on the air regulator bellows. Operation of the motor and consequent rotation of the counterweight superimposed on the motion of the bellows an oscillatory motion which produced the desired periodic variation in air pressure to provide the tremolo effect, without the loss of air experienced with dump valves. Although this was in some ways an improvement over the dumping valve arrangement, it was not entirely satisfactory since the rotation of the counterweight introduced not only vertical motion in the bellows, but horizontal components as well, since it was not possible to direct the force produced by the device at the center of the bellows. It was found that this multidirectional vagrant motion of the bellows resulted in a very high rate of wear on the bellows itself, which usually is made of leather or similar flexible material. Furthermore, because of this vagrant motion of the bellows, this device was very inefficient, required a large heavy motor for operation, and did not produce a good tremolo effect.
Another difficulty with this direct-mounted motor driven tremolo device was that the motor and counterweight assembly added a considerable amount of weight to the bellows structure, thus changing the resonant frequency of the bellows and affecting the overall pressure of the system.
An attempt to solve the difficulties experienced with the foregoing arrangement is illustrated in U.S. Pat. No. 3,018,682 to Imhoff, which utilizes a motor-driven cam wheel to produce tremolo effects. The cam wheel is connected to the bellows of an air pressure regulator by means of a drive rod connected to one end of a lever arm which extends across the top of the bellows. The center of the lever arm is connected to the bellows and the free end carries a lead weight. Rotation of the cam wheel causes the drive rod to move vertically, and causes the lever arm to pivot around its midpoint connection to the bellows. The lead weight on the free end of the lever arm provides inertia in the lever arm which thereby causes the bellows to be vertically displaced by the rotation of the cam wheel, with the size of the lead weight determining the amplitude of this displacement.
Although the Imhoff device represented an improvement over the prior motor-driven tremolo device in that it reduced the amount of vagrant motion in the bellows, the Imhoff device may introduce other problems, for the numerous bearings required in the rod and lever arm arrangement can produce an unacceptable noise problem as the bearings wear. Furthermore, arrangements such as Imhoff do not entirely eliminate the vagrant motion of the bellows since the rotation of the cam wheel and the resultant pivotal motion of the drive rod may introduce a horizontal component in the drive force supplied to the bellows. In addition, the drive mechanism for Imhoff is large and must be mounted beside the air pressure regulator, thus requiring an excessive amount of space in an area where space is usually at a premium, for most organ installations are located in crowded quarters.